It's not working for me either, on FFmpeg 7.0.2. I suspect something has changed in FFmpeg since that command was shared on the Reddit post mentioned on the website. That was a few years ago.
However, from the same Reddit thread, this works:
ffmpeg -v quiet -f data -i input.txt -map 0 -f data pipe:1
EDIT: just verified the `-c text` approach works on FFmpeg major versions 4 and 5. From FFmpeg 6 onwards, it's broken. The `pipe:1` method works from FFmpeg 5 onwards, so the site should probably be updated to use that instead (also, FFmpeg 5.1 is an LTS release).
However, from the same Reddit thread, this works:
ffmpeg -v quiet -f data -i input.txt -map 0 -f data pipe:1
EDIT: just verified the `-c text` approach works on FFmpeg major versions 4 and 5. From FFmpeg 6 onwards, it's broken. The `pipe:1` method works from FFmpeg 5 onwards, so the site should probably be updated to use that instead (also, FFmpeg 5.1 is an LTS release).